As the leader of the Bolshevik Party, Vladimir Lenin was the architect of the October Revolution, which brought the Bolsheviks to power. Lenin's ideology was grounded in Marxism, but he adapted it to fit the specific conditions in Russia, developing what became known as Marxism-Leninism. Under Lenin's leadership, the new Soviet government sought to redistribute land, nationalize industry, and establish a dictatorship of the proletariat. Although he died in 1924, Lenin's ideas laid the ideological foundation for the Soviet state. His emphasis on one-party rule, centralization of power, and suppression of opposition became hallmarks of the USSR. 

A prominent revolutionary and close ally of Lenin, Leon Trotsky played a crucial role in the Red Army's success during the Russian Civil War (1917-1923). As the People's Commissar for Military and Naval Affairs, Trotsky's leadership and organizational skills helped secure the Bolsheviks' victory over anti-communist forces. He was also an influential Marxist theorist, advocating for the idea of permanent revolution – a concept that emphasized the need for continuous, international socialist revolutions. However, after Lenin's death, Trotsky lost a power struggle to Joseph Stalin and was eventually exiled. His subsequent criticism of Stalinism made him a controversial figure, and he was assassinated in 1940 in Mexico, under orders from Stalin. 

1. Joseph Stalin, who became the General Secretary of the Communist Party in 1922, emerged as Lenin’s successor, consolidating power by the late 1920s. Stalin's leadership marked a significant departure from Lenin's policies, with an emphasis on rapid industrialization, collectivization of agriculture, and the establishment of a totalitarian state. His Five-Year Plans transformed the Soviet Union into a major industrial power, but at great human cost, including the Holodomor famine in Ukraine and the widespread purges of the Great Terror during the 1930s, which resulted in the execution or imprisonment of millions of people. Stalin's impact on the USSR was immense, as his policies shaped the country’s economy, politics, and society throughout his rule, which lasted until his death in 1953.